Modular semi-active joint exoskeleton

ABSTRACT

Systems, methods, and apparatus provide artificial knees. Artificial knees include a thigh link configured to move in unison with a thigh of the person, a shank link configured to be rotatably coupled to said thigh link, and a compression spring rotatably coupled to the thigh link and coupled to a second end of shank link with a second end of the compression spring. During a first range of motion, the compression spring is configured to provide an extension torque between the thigh link and the shank link causing said artificial knee to resist flexion. After said first range of motion, the compression spring is configured to provide a flexion torque between the thigh link and the shank link encouraging said artificial knee to flex resulting in toe clearance during the swing phase. During the swing phase, the compression spring provides no torque between the thigh link and the shank link.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 15/898,102,filed on May 15, 2018, which claims the benefit under 35 U.S.C. § 119(e)of U.S. Provisional Patent Application No. 62/459,564, filed on 2017Feb. 15, which are incorporated herein by reference in its entirety forall purposes.

STATEMENT OF GOVERNMENT SUPPORT

This invention was made with government support under Contract No.1545106 awarded by the National Science Foundation. The government hascertain rights in this invention.

TECHNICAL FIELD

The present disclosure pertains to artificial lower limb prosthetics andorthotic systems and more particularly, to an exoskeleton knee that canbe used for a variety of orthotic applications.

BACKGROUND

A traditional knee-ankle-foot orthosis (KAFO) is used to increase thepatient stability during the weight-bearing phase of walking. Atraditional KAFO locks the knee in full extension, which providesstability. This locked posture results in patients' ability to ambulatewith gait deviations that can lead to overuse injuries. A stance controlorthosis (SCO) allows the knee to flex during the swing phase of thegait cycle and prevents knee flexion for stability during the stancephase. By allowing the knee to bend during the swing phase, SCOs allow amore natural gait, which may reduce secondary complications from gaitcompensations and allow the patient to walk with less effort.

FILLAUER® developed a gravity-actuated knee joint locking system for itsSwing Phase Lock (SPL) orthosis (U.S. Patent 2003/0153854). A SwingPhase Lock uses a simple internal pendulum mechanism mounted on thethigh link (the member that moves in unison with the user's thigh). Asthe thigh link moves, the pendulum swinging motion locks and unlocks theshank link (the member that moves in unison with the user's shank)relative to the thigh link. This allows for locking and unlocking of theknee joint for appropriate phases of a walking cycle.

Free Walk orthosis (marketed by OTTOBOCK®) and UTX orthosis (marketed byBECKER®) work based on the principle. The dorsiflexion of the foot atthe end of the stance pulls on controllable cable connected to a lockingmechanism at the knee joint. This pulling action disengages the lockingmechanism for swing. The locking mechanism is spring loaded and locksthe knee when the knee is fully extended.

Sensor Walk (manufactured by OTTOBOCK®) uses a wrap spring at the kneejoint for locking and unlocking the knee. This orthosis includes twosets of sensors—one at the knee to measure the knee angle and another atthe footplate to measure force between the foot and the floor; a wrapspring clutch replacing the lateral knee joint to provide brakingcapability to support the anatomic knee joint; amicroprocessor-controlled release for the brake; electronic circuitry;and a battery pack carried in a waist pack. Sensors in the footplatedisengage the wrap spring clutch and allow the knee to bend in the latestance phase, when weight has been transferred to the contralateral sideand is ready for single-limb support. A knee sensor senses extension ofthe knee after toe off and sends a signal to the microprocessor puttingthe wrap spring clutch in its locked position.

Horton Stance Control Orthosis (U.S. Pat. No. 6,635,024) includes alocking mechanism that locks and unlocks the knee with the help of apush rod. The push rod is placed between the heel and the knee. The pushrod locks the knee at heel strike and unlocks the knee right at the endof stance phase. The device locks knee at any angle.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts an embodiment of artificial knee 100 associated withperson 200.

FIG. 2 depicts knee angle θ_(KNEE) 700 during a walking cycle.

FIG. 3 depicts an embodiment of artificial knee 100.

FIG. 4A, FIG. 4B, FIG. 4C, and FIG. 4D depict when thigh link 102 movesfrom one singular point to another.

FIG. 5A and FIG. 5B depict how artificial knee 100 provides support froma first singular point to a second singular point, and does not providesupport from the second singular point to the first singular point.

FIG. 6 depicts artificial knee 100 in a configuration as a toggleswitch.

FIG. 7A, FIG. 7B, FIG. 7C, FIG. 7D, FIG. 7E, and FIG. 7F depict howartificial knee 100 operates in a gait cycle.

FIG. 8 depicts individual states of artificial knee 100 in a gait cycleas a function of knee angle θ_(KNEE) 700.

FIG. 9 depicts the finite state machine of artificial knee 100.

FIG. 10A, FIG. 10B, FIG. 10C, and FIG. 10D depict artificial knee 100,in one embodiment, having extension link 112 which allows knee angleθ_(KNEE) 700 to have a larger range of motion without impeding theoperation in a gait cycle.

FIG. 11 depicts one embodiment of a mechanical configuration.

FIG. 12 depicts a cross-sectional view of the mechanical configurationas shown in FIG. 11.

FIG. 13 depict a mechanical configuration as shown in FIG. 12 with anindication of the rotating axes of four bar linkage 130.

FIG. 14 depicts a cross-sectional view of the mechanical configurationshown in FIG. 11 focusing on adjustment mechanism 132.

FIG. 15 shows how adjustment mechanism 132 can affect engagement angle802.

FIG. 16 shows how adjustment mechanism 132 can affect engagement angle802 while adjuster 110 is moved in direction 606.

FIG. 17, FIG. 18, FIG. 19, FIG. 20. FIG. 21, and FIG. 22 depict howartificial knee 100 operates in a gait cycle in a cross-sectional viewof the mechanical configuration in FIG. 11.

FIG. 23 depicts a cross-sectional view of the mechanical configurationof FIG. 11 when the knee angle θ_(KNEE) 700 is 90 degrees.

FIG. 24 depicts a torque profile of an embodiment of artificial knee100.

FIG. 25A and FIG. 25B depict an embodiment of artificial knee 100 wheretoggle angle 804 is adjustable.

FIG. 26 shows an embodiment of artificial knee 100 worn by person 200 asan orthotics knee, and additionally shows artificial knee 100 coupled toankle-foot orthotics 210.

FIG. 27 shows an embodiment of artificial knee 100 worn by person 200 asan exoskeleton knee.

FIG. 28 shows an embodiment of artificial knee 100 worn by person 200 asa prosthetics knee.

FIG. 29A and FIG. 29B depict how when adjuster 110 changes the distancebetween joint C 141 and knee joint 140, engagement angle 802 and releaseangle 806 can be adjusted.

DETAILED DESCRIPTION

FIG. 1 shows the schematic of leg 200 of a person. Knee angle θ_(KNEE)700 is defined as an angle between the extension of human thigh relativeto the human shank as shown in FIG. 1. In various embodiments, the humanknee extends if knee angle θ_(KNEE) 700 gets smaller. The human kneeflexes if knee angle θ_(KNEE) 700 gets larger. Accordingly, “kneeextension” or “extending the knee” refer to the situations where thehuman leg intends to straighten. Similarly, “knee flexion” or “flexingthe knee” refer to the situations where the human leg intends to bend.

FIG. 2 shows the plot of human knee angle, θ_(KNEE) 700, during awalking cycle. As seen in FIG. 2 there are two main phases in a gaitcycle, a stance phase and a swing phase. The stance phase refers to theconfigurations when the foot is on the ground, and the swing phaserefers to the configurations when the foot is off the ground. The swingphase can be subdivided into two phases: swing flexion—when the kneeflexes, and swing extension—when the knee extends. In summary the gaitcycle starts at foot strike. Later, the human leg enters the swing phaseat toe off. The swing phase starts with a swing flexion phase, followedby the swing extension phase. As can be seen in FIG. 2, human kneeangle, θ_(KNEE) 700, during the entire walking cycle, flexes to localminimums twice: once during the stance phase and once during the swingphase. During the stance phase the knee angle increases (flexes) toθ_(MAX,ST). During the swing phase, the knee reaches maximum kneeflexion θ_(MAX). θ_(TO) represents the knee angle at the toe off. Theknee reaches the minimum knee angle θ_(MIN) toward the end of swingphase. Although there may be variation from the plot shown in FIG. 2,generally the human knee goes through two flexions in a walking cycle: asmall flexion during the stance phase and a large one during the swingphase. The small flexion is in response to the person's weight while thelarger flexion provides toe clearance during the swing phase.

Artificial knee 100 (which may be either a prosthetic knee or anorthotic knee) is configured to exhibit the basic behavior of the humanknee with no actuators, sensors and computers. Such a knee can be usedas a low cost artificial knee 100 for various orthotic, prosthetic andexoskeleton applications. As shown in FIG. 1, artificial knee 100comprises a thigh link 102, shank link 104, rotatably coupled to eachother at knee joint 140. Based on the observation described above inFIG. 1 and FIG. 2, the artificial knee 100 is configured to exhibitthree behaviors: (1) artificial knee 100 is configured to resist theknee flexion during the stance phase (this means artificial knee 100helps the human during the stance phase to support a portion of user'sweight); (2) artificial knee 100 is configured to encourage knee flexionduring the swing phase to assist in toe clearance during the swingflexion phase; and (3) artificial knee 100 is configured to allow freeswing extension in the swing extension phase.

The above three features facilitate the artificial knee 100 to supportthe user during the stance phase, but remain free during the swingextension. It further encourages the knee flexion right at early swingphase. In various embodiments, all of the above features are achievedpassively without the use of actuators, computers and sensors.

Accordingly, artificial knee 100 is configured to produce an extensiontorque from engagement angle 802 (represented by θ_(ENG) in FIG. 2) totoggle angle 804 (represented by θ_(TOG) in FIG. 2). This meansartificial knee 100 resists flexion and assists the user during thestance phase to support at least a portion of the user's weight.Extension torque is defined as a torque that causes artificial knee 100to extend. Artificial knee 100 is further configured to provide flexiontorque from toggle angle θ_(TOG) 804 to release angle 806 (representedby θ_(REL) in FIG. 2). This means artificial knee 100 encourages kneeflexion during the swing phase to assist in toe clearance. Flexiontorque is defined as a torque that causes artificial knee 100 to flex.In FIG. 1, flexion torque is a torque that causes θ_(KNEE) to increase.θ_(TOG) represents a knee angle that torque in the artificial knee 100switches (toggles) from an extension torque to a flexion torque. Theextension torque is needed to support the weight, while the flexiontorque is needed to clear the ground. Once the knee has accomplished theabove two features, it then needs to freely extend and get ready forfoot strike as shown in FIG. 2. This means the mechanism that createdextension torque between θ_(ENG) and θ_(TOG), and flexion torque betweenθ_(TOG) and θ_(REL) is configured to become ineffective when the knee isextending before foot strike. Accordingly, artificial knee 100 isconfigured to first provide extension torque from engagement angleθ_(ENG) 802 to toggle angle θ_(TOG) 804 and then provide flexion torquefrom toggle angle θ_(TOG) 804 to release angle θ_(REL) 806. In someembodiments, artificial knee 100 does not need to provide any othertorque in any other phases of the knee trajectory. The state whenartificial knee 100 provides extension torque is called the “extensionsupport state”. Similarly, the state when artificial knee 100 providesflexion torque is called “flexion support state”.

To design artificial knee 100, one must specify angles θ_(ENG), θ_(TOG),θ_(REL) (represented by 802, 804, and 806). θ_(ENG), θ_(TOG), θ_(REL)angles correspondingly represent when the extension torque should begin,when the extension torque should switch to flexion torque, and when theflexion torque should end. The range limits of angles 802, 804, and 806are defined by three inequalities: (1) θ_(MIN)<θ_(ENG)<θ_(MAX,ST); (2)θ_(MAX,ST)<θ_(TOG)<θ_(TO); and (3) θ_(TO)<θ_(REL)<θ_(MAX).

As shown in FIG. 2, θ_(MIN) is the minimum knee angle during the gait,θ_(MAX,ST) is the maximum knee angle in the stance phase, θ_(TO) is kneeangle at toe off, and θ_(MAX) is the maximum knee angle throughout thegait.

If θ_(ENG)>θ_(MAX,ST), artificial knee 100 provides no resistance duringsome portion of stance phase. If θ_(REL)<θ_(TO), toe clearance will notbe encouraged. In various embodiments, θ_(TOG) 804 is configured to bethe same as the knee angle at toe off so flexion torque is generated assoon as toe off takes place. To prevent any extension torque after toeoff (because it might hinder knee flexion), θ_(TOG) 804 is configured tobe smaller than the average knee angle at toe off. Extension torqueafter toe off will prevent knee flexion needed for ground clearance. Invarious embodiments, the average minimum knee angle at toe off isapproximately 35 degrees. Therefore, in one embodiment, θ_(TOG) 804 isconfigured to be 30 degrees. Such a configuration of θ_(TOG) 804guarantees that toggle point of artificial knee 100 takes place beforethe toe off. It will be appreciated that other values for θ_(TOG) 804may be implemented depending on the applications and other specificissues related to the user. In some embodiments, θ_(ENG) 802 isconfigured to be as small as possible and θ_(REL) 806 is configured tobe as large as possible to create more supportive torque. However(θ_(REL)−θ_(ENG)) is within the range of normal knee operation range.This means (θ_(REL)−θ_(ENG))<(θ_(MAX)−θ_(MIN)).

In some embodiments, θ_(MIN), θ_(MAX,ST) and θ_(MAX) are around 0, 20and 65 degrees, respectively. Considering various gaits for differentindividuals, in some embodiments, artificial knee 100 may be configuredsuch that θ_(ENG) 802 and θ_(REL) 806 are 5 and 55 degrees,respectively. It will be appreciated that other values for θ_(ENG) 802and θ_(REL) 806 may be implemented depending on the applications andother specific issues related to the user.

FIG. 3 shows the schematic of an embodiment of artificial knee 100.Artificial knee 100 comprises thigh link 102, and shank link 104rotating about knee joint 140. Knee angle θ_(KNEE) 700 represents theangle between shank link 104 and the extension of thigh link 102. Sincein orthotic and prosthetic applications, the human knee angle and theartificial knee angle coincide on each other. θ_(KNEE) 700 is used torepresent both the angle of human knee and the angle of artificial knee100. In some embodiments, such as exoskeletons or orthotic systems,thigh link 102 and shank link 104 are designed to move in unison withthe human's thigh and shank. Thigh brace 206 as shown in FIG. 26 andFIG. 27 is used to couple thigh link 102 to person's thigh. In someembodiments, as shown in FIG. 26 and FIG, 27, shank brace 208 is used tocouple shank link 104 to person's shank.

FIG. 3 shows that artificial knee 100 further comprises compressionspring 106 rotatably coupled to thigh link 102 from its first end 510.Artificial knee 100 further comprises fourth link 108 rotatably coupledwith the second end 511 of compression spring 106. Compression spring106, fourth link 108 in addition to shank link 104 and thigh link 102form four bar linkage 130 as shown in FIG. 3. Below describes how thisfour bar linkage achieves the above features mentioned above. In someembodiments, thigh link 102 and shank link 104 may be considered as adriver link and ground link of the four bar linkage 130 respectively.Further, compression spring 106 and fourth link 108 may be consideredthe coupler link and the follower link of four bar linkage 130.Transmission angle μ 702 is defined as the angle between fourth link 108and compression spring 106 as shown in FIG. 3. When compression spring106 is not compressed and it acts like a rigid link, this mechanism is arocker-rocker four-bar linkage, which means that both driver link (thighlink 102) and follower link (fourth link 108) have reciprocating motion.Constraint 118 is fixed on shank link 104 to stop the rotation of fourthlink 108 (follower link) at a certain angle. Constraint 118 can be ahard stop formed on shank link 104. In some embodiments, constraint 118is assumed to be parallel with fourth link 108 when it blocks fourthlink 108.

The range of motion of the thigh link 102 (driver link of four barlinkage 130) is defined by the singular points where compression spring106 (coupler link for four bar linkage 130) aligns with fourth link 108(i.e., transmission angle μ 702 is 0). FIG. 4A through FIG. 4D showseveral properties of four bar linkage 130. FIG. 4A shows artificialknee 100 when thigh link 102 moves from one singular configuration A₁ toanother singular configuration A₂. At each singular configuration,fourth link 108 has two options to move: it can either follow trajectory160 in FIG. 4A or follow trajectory 162 shown in FIG. 4B. Singularconfigurations are the only points that fourth link 108 has these twooptions, FIG. 4A and FIG. 4B show configurations where thigh link 102moves from A₁ counter-clockwise to A₂. Fourth link 108 is initiallylocated at singular point B₁. If fourth link 108 is perturbed to startmoving counter-clockwise as shown in FIG. 4A, then trajectory 160 showshow fourth link 108 moves from B₁ to B₂. FIG. 4B shows the samemechanism where thigh link 102 moves from A₁ to A₂, however fourth link108 is initially perturbed to a clockwise direction where it moves fromB₁ to B₂ along trajectory 162. FIG. 4C and FIG. 4D show configurationswhere thigh link 102 moves clockwise from A₂ to A₁. Fourth link 108 isinitially located at singular point B₂. If fourth link 108 is perturbedto start moving counter-clockwise as shown in FIG. 4C, then trajectory164 shows how fourth link 108 moves from B₂ to B₁. FIG. 4D shows thesame mechanism where thigh link 102 moves from A₂ to A₁ clockwisehowever fourth link 108 is initially perturbed to a clockwise directionwhere it moves from B₂ to B₁ along trajectory 166.

Turning to FIG. 4B and FIG. 4C, the operation of four bar linkage 130 isdescribed when fourth link 108 (follower link) is perturbed to travelalong trajectory 162 when thigh link 102 travels from A₁ to A₂, andalong trajectory 164 when thigh link 102 travels back from A₂ to A₁. Asshown in FIG. 4B, fourth link 108 is perturbed to move along trajectory162 at point B₁. While thigh link 102 moves from A₁ to A₂counter-clockwise, fourth link 108 (follower link) moves from B₁ to B₂and to B₄, and then back to B₂ along trajectory 162. If fourth link 108is perturbed to go along trajectory 164 (as shown in FIG. 4C), thenfourth link 108 moves from B₂ to B₁ and to B₃ and then back to B₂ alongtrajectory 164, when thigh link 102 moves from A₂ to A₁ in clockwisedirection. FIG. 4B and FIG. 4C show how four bar linkage 130 operatesfor an entire cycle of thigh link 102, if fourth link 108 is perturbedat point B₁ and B₂ along trajectories 162 and 164.

In some embodiments, constraint 118 is placed to block fourth link 108between B₂ and B₄, as shown in FIG. 5. FIG. 5A represents artificialknee 100 when thigh link 102 rotates counter-clockwise from A₁ to A₂.FIG. 5B represents artificial knee 100 when thigh link 102 rotatesclockwise from A₂ to A₁. When thigh link 102 moves from A₁ to A₂counter-clockwise (as shown in FIG. 5A), constraint 118 blocks fourthlink 108. B₁₀ represents joint B when fourth link 108 (follower link)becomes constrained. Similarly A₁₁ represents joint A when fourth link108 (follower link) becomes constrained. Since coupler link (compressionspring 106) is compressible, as thigh link 102 continues to moveclockwise, coupler link (compression spring 106) gets compressed andresists the rotation of thigh link 102 relative to shank link 104.Points a, b, and c represent the locations of joint A when thigh link102 travels from A₁₁ to A₁₂ while fourth link 108 (follower link) is notmoving. When thigh link travels from A12 to A2, fourth link 108(follower link) travels from B₁₀ to B₂. A small torque applying on thefourth link 108, when fourth link 108 is at B₂, pushes fourth link 108away from constraint 118. At this time, when thigh link 102 moves backfrom A₂ clockwise (as shown in FIG. 5B), fourth link 108 moves alongtrajectory 164 with no constraint as shown in FIG. 5B. This means thighlink 102 moves from A₂ to A₁ through points d, e, and f with noresistance from compression spring 106. Once thigh link 102 reachespoint A₁, another small torque pushes fourth link 108 at B₁ to be ontrajectory 162. The behavior described above represents a situationwhere when thigh link 102 moves from A₁ to A₂, it will experienceresistance from compression spring 106; however, from A₂ to A₁ thighlink 102 will not experience any resistance from compression spring 106.

FIG. 6 shows artificial knee 100 as shown in FIG. 5A. Points A₁₁ and A₁₂represent the locations of thigh links 102 when follower link (fourthlink 108) is constrained. Both thigh link 102 and compression spring 106(coupler link) are shown by dashed lines in these boundary locationswhere fourth link 108 (follower link) is constrained. As can be seen inFIG. 6, compression spring 106 starts to compress and resist the motionof thigh link 102 when thigh link 102 is at point A₁₁. This compressioncontinues until joint A reaches point b where compression spring is atits shortest length. This means from A₁₁ to b, compression spring 106provides extension torque for artificial knee 100. After point b, whenthigh link 102 travels toward A₁₂, compression spring 106 switches itsextension torque to flexion torque. This means the flexion motion ofthigh link 102 from b to A₁₂ is encouraged by compression spring 106. Asshown in FIG. 6, when fourth link 108 (follower link) is constrained,compression spring 106 (coupler link) provides a compression force thatpasses through the coupling location of thigh link 102 relative to shanklink 104 (joint 140) when thigh link 102 is at point b (toggle point).At point b, thigh link 102 and compression spring 106 are aligned andcompression spring 106 is at its shortest length. The toggle point, b,is an unstable equilibrium point for compression spring 106. When thighlink 102 moves from A₁₁ toward point b, compression spring 106 providesan extension torque between thigh link 102 and shank link 104. Whenthigh link 102 moves from b toward point A₁₂, compression spring 106provides a flexion torque between thigh link 102 and shank link 104.

As described above, at singular points (point B₁ and B₂), small torquesare applied to fourth link 108 to perturb fourth link 108 to move alongtrajectories 162 and 164 because driver link (thigh link 102) loses itsability to move four bar linkage 130. These torques are provided byfirst and second leaf springs 120 and 122 as described below.

The operation of artificial knee 100 in a gait cycle is shown in FIG. 7.FIG. 7A shows that artificial knee 100 is at a singular point wherecoupler link (compression spring 106) aligns with the follower link(fourth link 108). Joint A is located at point A₁ and joint B is locatedat B₁. Knee angle 700 at this instance is defined as start angleθ_(START) 800. With the application of a small torque along direction600 on follower link (fourth link 108), follower link (fourth link 108)moves clockwise to break away from singular point and ultimatelytransition the transmission angle μ to a negative value.

As thigh link rotates counter-clockwise (artificial knee 100 flexes),follower link (fourth link 108) rotates toward constraint 118 untilfourth link 108 (follower link) encounters constraint 118 as shown inFIG. 7 (B). Joint B is located at point B₁₀ and joint A is A₁₁. At thispoint, compression spring 106 begins to provide an extension torque asartificial knee 100 continues to flex. Knee angle θ_(KNEE) 700, at thisinstance is called engagement angle θ_(ENG) 802 where the “extensionsupport state” starts.

When thigh link 102 continues to rotate counter clockwise, there is apoint where thigh link 102 aligns with coupler link (compression spring106) as shown in FIG. 7C. At this point, the extension torque generatedby coupler link (compression spring 106) switches its direction andbecomes a flexion torque. The knee angle θ_(KNEE) 700 at this instanceis called toggle angle θ_(TOG) 804 where the “flexion support state”starts. Joint A 300 is located at point b where the compression force ofcompression spring 106 passes through knee joint 140.

The flexion torque exists until coupler link (compression spring 106)reaches its original length as shown in FIG. 7(D). Knee angle θ_(KNEE)700, at this point, is defined as the release angle θ_(REL) 806 Joint Ais at point A₁₂.

Thigh link 102 continues to rotate counter-clockwise until it reachesanother singular point when knee angle θ_(KNEE) 700 is at end angleθ_(END) 808 as shown in FIG. 7 (E). At this instance joint A is at pointA₂ and joint B is at point B₂. At this instance, a small torque onfollower link (fourth link 108), along direction 602, causes followerlink (fourth link 108) to rotate away from constraint 118. Transmissionangle μ at this time switches from negative to positive.

During knee extension as shown in FIG. 7F, thigh link 102 rotatesclockwise, and follower link (fourth link 108) rotates away fromconstraint 118. No torque resists thigh link 102 clockwise motion. Thighlink 102 rotates clockwise (knee extension) and returns back to theconfiguration shown in FIG. 7A where artificial knee 100 is again at asingular point at which the transmission angle μ is on the verge ofshifting signs.

The configuration of artificial knee 100 between FIG. 7E and FIG. 7A isconsidered the first free state because thigh link 102 encounters noresistance when it rotates clockwise. The configuration of artificialknee 100 between FIG. 7A and FIG. 7B is considered the second free statebecause thigh link 102 again encounters no resistance when it rotatescounter-clockwise. The configuration of artificial knee 100 between FIG.7B and FIG. 7C is considered the extension support state becausecompression spring 106 provides extension torque between thigh link 102and shank link 104. The configuration of artificial knee 100 betweenFIG. 7C and FIG. 7D is considered the flexion support state becausecompression spring 106 provides flexion torque between thigh link 102and shank link 104. The configuration of artificial knee 100 betweenFIG. 7D and FIG. 7E is considered the third free state because thighlink 102 encounters no resistance when it rotates counter clockwise.

FIG. 8 depicts the states of artificial knee 100 defined above.Artificial knee 100 is in the first free state when it is flexing andknee angle θ_(KNEE) 700 is not larger than start angle θ_(START) 800.Artificial knee 100 is in the second free state when it is flexing andknee angle θ_(KNEE) 700 is between start angle θ_(START) 800 andengagement angle θ_(ENG) 802. Artificial knee 100 is in the extensionsupport state when knee angle θ_(KNEE) 700 is between engagement angleθ_(ENG) 802 and toggle angle θ_(TOG) 804. Artificial knee 100 is in theflexion support state when it is flexing and knee angle θ_(KNEE) 700 isbetween toggle angle θ_(TOG) 804 and release angle θ_(REL) 806.Artificial knee 100 is in the third free state when knee angle θ_(KNEE)700 is between release angle θ_(REL) 806 and end angle θ_(END) 808.

FIG. 9 depicts the behavior of artificial knee 100 as a finite statemachine. The solid lines show when artificial knee 100 is operatednormally as knee angle θ_(KNEE) 700 follows the data as shown in FIG. 8.

FIG. 10 depicts artificial knee 100, in one embodiment, having extensionlink 112 that allows knee angle θ_(KNEE) 700 to expand larger than theknee angle at the singular configurations, i.e., start angle θ_(START)800 and then end angle θ_(END) 808. In one embodiment, extension link112 can be an extension spring that is capable of lengthening thecoupler but always tends to return the coupler to its shortest length.Extension link 112 acts as a rigid link when it is not pulled so theaforementioned operation is not affected, but becomes extendable whenthe knee reaches outside the boundary of the singular configurations.

FIG. 10A and FIG. 10B show one embodiment of artificial knee 100 withextension link 112, where the first end of extension link 112 isrotatably coupled to thigh link 102, and the second end of extensionlink 112 is linearly coupled to the first end 510 of compression spring106. FIG. 10A depicts artificial knee 100 with extension link 112 thatallows knee angle θ_(KNEE) 700 to be about 0 degrees. FIG. 10B depictsartificial knee 100 with extension link 112 that allows the knee angleθ_(KNEE) 700 to be about 90 degrees.

FIG. 10C and FIG. 10D show another embodiment of artificial knee 100with extension link 112, where the first end of extension link 112 isrotatably coupled to the second end 511 of compression spring 106, andthe second end of extension link 112 is linearly coupled to followerlink (fourth link 108). FIG. 10C depicts artificial knee 100 withextension link 112 that allows knee angle θ_(KNEE) 700 to be about 0degrees. FIG. 10D depicts artificial knee with extension link 112 thatallows knee angle θ_(KNEE) 700 to be about 90 degrees.

FIG. 11 shows an embodiment of artificial knee 100 which is designedbased on the embodiments described above. FIG. 12 depicts across-sectional view of the mechanical configuration shown in FIG. 11.FIG. 13 is the same as FIG. 12, however it also shows all axes ofrotations related to four bar linkage 130. In this embodiment, extensionlink 112 is rotatably coupled with thigh link 102, and linearly coupledwith compression spring 106. Referring to FIG. 11, FIG. 12 and FIG. 13,artificial knee 100 comprises thigh link 102 configured to move inunison with the person's thigh. Artificial knee 100 further comprisesshank link 104 which is configured to move in unison with the person'sshank and rotatably coupled to thigh link 102. Thigh link 102 and shanklink 104 rotate relative to each other about knee joint 140. Axis 142represents the axis of knee joint 140 (rotation of thigh link 102relative to shank link 104). Artificial knee 100 further comprises acompression spring 106 which is rotatably coupled to thigh link 102 atjoint A 300. Axis 144 in FIG. 13 represents the rotation axis of joint A300 (compression spring 106 relative thigh link 102). Compression spring106 is rotatably coupled with fourth link 108 (follower link) from itssecond end 512 at Joint B 400. Axis 145 represents the rotational axisof joint B 400 (rotation of fourth link 108 relative compression spring106). Fourth link 108 is rotatably coupled to shank link 104 at Joint C141. Axis 143 represents the axis of joint C 141 (rotation of fourthlink 108 relative to shank link 104).

FIG. 15 depicts a cross-sectional view of the mechanical configurationin FIG. 11. FIG. 15 is similar to FIG. 13, but focuses on first leafsprings 120 and second leaf spring 122. In this embodiment, artificialknee 100 further comprises first leaf spring 120. The first end of firstleaf spring 120 is coupled to shank link 104, and the second end offirst leaf spring 120 is configured to provide torque in direction 602on follower link (fourth link 108). First leaf spring 120 causes fourthlink 108 (follower link) to move along trajectory 164 as shown in FIG.5B. Artificial knee 100 further comprises second leaf spring 122. Thefirst end of second leaf spring 122 is coupled to shank link 104, andthe second end of second leaf spring 122 is configured to provide torquein direction 600 on follower link (fourth link 108). Second leaf spring122 causes fourth link 108 (follower link) to move along trajectory 162as shown in FIG. 5A. In some embodiments, first leaf spring 120 andsecond leaf spring 122 can be combined into one single spring, or othertype of torque generators such as magnet. Accordingly, first leaf spring120 and second leaf spring 122 are configured to create torques causingfollower link (fourth link 108) to move along trajectories 164 and 166.

As shown in FIG. 14, artificial knee 100 further comprises constraint118. Constraint 118 is coupled to shank link 104. In some embodiments,constraint 118 is manufactured as a feature included in shank link 104.Constraint 118 blocks the motion of fourth link 108 when fourth link 108moves along trajectory 162 shown in FIG. 5A.

In some embodiments, as shown in FIG. 14, FIG. 15 and FIG. 16,artificial knee 100 further comprises an adjustment mechanism 132 tochange the length between knee joint 140 and joint C 141. Accordingly,adjustment mechanism 132 is configured to allow the user to change thelength of ground link (shank link 104) shown in FIG. 3. It will bediscussed in greater detail below how this adjustment mechanism 132allows various features of artificial knee 100. Adjustment mechanism 132comprises adjuster 110 rotatably coupled to fourth link 108 from firstend and slidably coupled to shank link 104 from another end. Theexternal threads of adjuster 110 pass through a hole in shank link 104.Adjustment mechanism 132 further comprises thumb nut 114 and lock nut116. By turning both thumb nut 114 and lock nut 116, adjuster 110 movesalong direction 604 and 606 relative to shank link 104. This means thelocation of rotary joint C 141 with respect to knee joint 140 can beadjusted. The combination of thumb nut 114 and lock nut 116 secureadjuster 110 to shank link 104. It will be appreciated that variousadjustment mechanisms may be implemented to change the length of groundlink (shank link 104). FIG. 16 shows when adjuster 110 has moved alongdirection 606 in comparison with the configuration shown in FIG. 15. Theengagement angle θ_(ENG) 802 in configuration of FIG. 16 is larger thanthe engagement angle θ_(ENG) 802 in configuration of FIG. 15.

FIG. 17 through FIG. 22 depict artificial knee 100 at various kneeangles throughout a gait cycle. FIG. 17 represents artificial kneedepicted in FIG. 7A. FIG. 17 represents the configuration when kneeangle θ_(KNEE) 700 is equal to start angle θ_(START) 800. In thisconfiguration, coupler link (compression spring 106) aligns withfollower link (fourth link 108). This configuration is schematicallyshown by FIG. 7A. Second leaf spring 122 pushes follower link (fourthlink 108) with a torque along direction 600. Artificial knee 100 is atthe border of the first free state and the second free state.

FIG. 18 depicts artificial knee 100 when fourth link 108 (follower link)is constrained (blocked) by constraint 118 and the compressive spring106 is about to be compressed. Knee angle θ_(KNEE) 700 in FIG. 18 isequal to engagement angle θ_(ENG) 802. Artificial knee 100, at thisinstance, is at the border of the second free state and the extensionsupport state. This configuration is schematically shown by FIG. 7B.After this instance, as knee angle θ_(KNEE) 700 increases, compressivespring 106 gets compressed (gets shorter) and provides extension torqueabout knee joint 140. FIG. 19 depicts artificial knee 100 when kneeangle θ_(KNEE) 700 is equal to toggle angle θ_(TOG) 804. Fourth link 108(follower link) is constrained by constraint 118 and compressive spring106 aligns with knee joint 140. The torque from compressive spring 106is zero at this instance and the compressive spring is at its maximumcompression force. Artificial knee 100 at this instance is at the vergeof the extension support state and the flexion support state. This isschematically shown in FIG. 7C. As knee angle θ_(KNEE) 700 increases,compressive spring 106 starts to provide flexion torque about knee joint140 to encourage knee flexion. FIG. 20 depicts artificial knee 100 whenknee angle θ_(KNEE) 700 is equal to release angle θ_(REL) 806. Fourthlink 108, at this point is free to move away from constraint 118.Compressive spring 106, at this instant, completes generatingcompressive force and it returns to its original length. Artificial knee100 at this instance is at the verge of the flexion support state andthird free state. This is schematically shown in FIG. 7D. As knee angleincreases after this instance, compressive spring 106 does not providetorque on knee joint 140.

In this embodiment, end angle θ_(END) 808 is very close to release angleθ_(REL) 806. Therefore, the knee θ_(KNEE) 700 is at release angleθ_(REL) 806, which are virtually the same as end angle θ_(END) 808 inthis embodiment as shown in FIG. 20, coupler link (compression spring106) also aligns with follower link (fourth link 108), and first leafspring 120 pushes the follower link (fourth link 108) to direction 602.The mechanism in this instance is also at the verge of the third freestate and the first free state. This is schematically shown in FIG. 7E.FIG. 21 depicts artificial knee 100 when knee angle θ_(KNEE) 700 islarger than end angle θ_(END) 808. The extension of the extension link112 allows knee angle θ_(KNEE) 700 to be able to go beyond end angleθ_(END) 808. Artificial knee 100 is in the first free state. As kneeangle θ_(KNEE) 700 returns back to end angle θ_(END) 808, first leafspring 120 pushes follower link (fourth link 108) in direction 602. FIG.22 depicts artificial knee 100 when knee angle θ_(KNEE) 700 returns backto start angle θ_(START) 800 while artificial knee 100 is in the firstfree state. FIG. 23 depicts artificial knee 100 when knee angle θ_(KNEE)700 is 90 degrees. Artificial knee 100 is in the first free state.

FIG. 24 depicts a torque profile of an embodiment of artificial knee100. In the first free state, the second free state, and the third freestate, artificial knee 100 provides no torque. In extension supportstate, artificial knee 100 provides extension torque that attempts todecrease knee angle θ_(KNEE) 700. In flexion support state, artificialknee 100 provides flexion torque that attempts to increase knee angleθ_(KNEE) 700.

In some embodiments, toggle angle θ_(TOG) 804 is not adjustable.However, in other embodiments, toggle angle θ_(TOG) 804 is configured tobe adjustable. The adjusting of the toggle angle is shown in FIG. 25Aand FIG. 25B. Different locations of rotating point of the first end 510of compressive spring 106 on the thigh link 102 provide options toswitch toggle angle θ_(TOG) 804. It will be appreciated that variousadjustment mechanisms may be implemented to change toggle angle θ_(TOG)804.

FIG. 26 shows an embodiment of artificial knee 100 wearing by person 200as an orthotics knee. FIG. 26 shows artificial knee 100 further connectsto an ankle-foot orthotics 210. In some embodiments, such as theembodiment shown in FIG. 26, an ankle-foot orthosis 210 is configured tobe coupled to a person's foot. In some embodiments, ankle-foot orthosis210 is connectable to shank link 104. It will be appreciated that manyforms of internal and external ankle-foot-orthoses may be implemented.In some embodiments, artificial knee 100 is coupled to person 200through thigh brace 206 and shank brace 208. Although braces have beenused to demonstrate the coupling of shank link 104 and thigh link 102 tothe person's thigh 202 and person's shank 204 as shown in FIG. 26, itwill be appreciated that many methods and devices can be implementedthat would cause thigh link 102 and shank link 104 to move in unisonwith person's thigh 202 and person's shank 204; coupling through shankand thigh braces is just one method of causing the unison movement.

FIG. 27 shows an embodiment of artificial knee 100 wearing by person 200as an exoskeleton knee. FIG. 27 shows artificial knee 100 furtherconnects to exoskeleton 211 by connecting thigh link 102 to exoskeletonthigh 212, and shank link 104 to exoskeleton shank 214. In oneembodiment, exoskeleton thigh 212 and exoskeleton shank 214 moves inunison with person's thigh 202 and person's shank 204 via thigh brace206 and shank brace 208. In one embodiment, exoskeleton thigh 212 isrotatably coupled to exoskeleton trunk 216. In an alternative embodimentnot shown, exoskeleton thigh 212 is coupled to exoskeleton trunk 216 bymore than one rotary joints. It will be appreciated that exoskeletoncomponents may be implemented in different forms. Similar to orthotics,there are many methods and devices in the exoskeleton context that wouldenable thigh link 102 and shank link 104 to move with person's thigh 202and person's shank 204.

FIG. 28 shows an embodiment of artificial knee 100 worn by person 200 asa prosthetics knee. In one embodiment as shown in FIG. 28, thigh link102 connects with person's thigh 202 via socket 222. It will beappreciated that other methods and devices can be implemented that wouldcause thigh link 102 to move in unison with person's thigh 202. Shanklink 104 connects to an artificial shank 218. In one embodiment as shownin FIG. 28, artificial shank 218 further connects to artificial foot220. In an alternative embodiment not shown, artificial shank 218comprises a leaf spring that is design to contact with the ground withcompliancy. It will be appreciated that artificial shank 218 may beimplemented in many different forms.

FIG. 29 depicts how when adjuster changes the distance between joint C141 and knee joint 140, engagement angle 802 and release angle 806 canbe adjusted as discussed in FIG. 15 and FIG. 16. FIG. 29B depicts thesituation when adjuster 110 moved along direction 606 (shown in FIG. 14)compared to FIG. 29A. This means the length of ground link (shank link104) is becoming larger from FIG. 29A to FIG. 29B. As shown in FIG. 29,the difference between release angle 806 (at which thigh link is at A₁₂)and engagement angle 802 (at which thigh link is at A₁₁) becomessmaller.

What is claimed is:
 1. An artificial knee configured to be worn on a legof a person to provide resistance during the stance phase and freemotion during the swing phase, said artificial knee comprising: a thighlink configured to move in unison with a thigh of the person; a shanklink configured to be rotatably coupled to said thigh link at a firstend of the shank link; and a compression spring rotatably coupled to thethigh link with a first end of the compression spring and coupled to asecond end of shank link with a second end of the compression spring,wherein during a first range of motion of the thigh link and the shanklink relative to each other which takes place after said leg strikes theground, the compression spring is configured to provide an extensiontorque between the thigh link and the shank link causing said artificialknee to resist flexion, wherein after said first range of motion of thethigh link and the shank link relative to each other, the compressionspring is configured to provide a flexion torque between the thigh linkand the shank link encouraging said artificial knee to flex resulting intoe clearance during the swing phase, and wherein during the swingphase, the compression spring provides no torque between the thigh linkand the shank link.
 2. The artificial knee of claim 1, wherein thecompression spring is configured to provide a force that passes througha coupling location of the thigh link relative to the shank link duringa stance phase.
 3. The artificial knee of claim 1, wherein thecompression spring is configured to: resist the flexion of the thighlink relative to the shank link during said first range of motion of thethigh link and the shank link relative to each other, and encourages theflexion of the thigh link relative to the shank link after said firstrange of motion of the thigh link and the shank link relative to eachother.
 4. The artificial knee of claim 1, wherein the shank link isconfigured to move in unison with a shank of the person.
 5. Theartificial knee of claim 1, wherein during the motion of the thigh linkand the shank link relative to each other, the compression spring isconfigured to provide a force that passes through the coupling locationof the thigh link relative to the shank link at the end of the firstrange of motion of the thigh link and the shank link relative to eachother.
 6. The artificial knee of claim 1, wherein the artificial kneefurther comprises: a follower link, wherein the compression spring iscoupled to the shank link through the follower link such that the thighlink, the shank link, the follower link and the compression spring forma four-bar linkage comprising rotary joints; and a constraint configuredto constrain the motion of the follower link relative to the shank linkat least during the first range of motion of the thigh link and theshank link relative to each other.
 7. The artificial knee of claim 1,wherein the constraint is configured to block the motion of the followerlink at a singular point, wherein the singular point is a point wherethe compression spring and the follower link are in line with eachother.
 8. An artificial knee configured to be worn by a person, theartificial knee comprising: a thigh link configured to move in unisonwith a thigh of the person; a shank link configured to be rotatablycoupled to said thigh link at a first end of the shank link; acompression spring rotatably coupled to the thigh link with a first endof the compression spring; a follower link, coupled to a second end ofthe compression spring from one end and to the second end of the shanklink from another end such that the thigh link, the shank link, thefollower link, and the compression spring form a four bar linkagecomprising four rotary joints; and a constraint configured to constrainthe motion of the follower link relative to the shank link during afirst range and a second range of motion of the thigh link and the shanklink relative to each other, wherein during said first range of motionof the thigh link and the shank link relative to each other which takesplace after said leg strikes the ground, the compression spring isconfigured to provide an extension torque between the thigh link and theshank link causing said artificial knee to resist flexion, and whereinduring said second range of motion of the thigh link and the shank linkrelative to each after which takes place after said first range ofmotion, the compression spring is configured to provide a flexion torquebetween the thigh link and the shank link encouraging said artificialknee to flex resulting in toe clearance during the swing phase.
 9. Anartificial knee configured to be worn by a person, the artificial kneecomprising: a thigh link configured to move in unison with a thigh ofthe person; a shank link configured to be rotatably coupled to saidthigh link at a first end of the shank link; a compression springrotatably coupled to the thigh link with a first end of the compressionspring; and a follower link, coupled to a second end of the compressionspring from one end and to the second end of the shank link from anotherend such that the thigh link, the shank link, the follower link, and thecompression spring form a four bar linkage comprising rotary joints; anda constraint configured to constrain a motion of the follower linkrelative to the shank link during a range of motion of the thigh linkrelative to the shank link, wherein at a point during the range ofmotion where the constraint blocks the motion of the follower link, thecompression spring is configured to provide a force such that the forcepasses through the coupling location of the thigh link and shank linkthereby switching the torque provided by the said force from extensiontorque to flexion torque.
 10. An artificial knee configured to be wornby a person, the artificial knee comprising: a thigh link configured tomove in unison with a thigh of the person; a shank link configured to berotatably coupled to said thigh link at a first end of the shank link; acompression spring rotatably coupled to the thigh link with a first endof the compression spring; a follower link, coupled to a second end ofthe compression spring from one end and to the second end of the shanklink from another end such that the thigh link, the shank link, thefollower link, and the compression spring form a four bar linkagecomprising rotary joints wherein a singular point is a point where thecompression spring and the follower link are in line with each other;and a constraint configured to constrain the motion of the follower linkrelative to the shank link during a range of motion of the thigh linkrelative to the shank link, wherein when the follower link is moved fromsaid singular point toward the constraint, the constraint blocks thefollower link, and the compression spring provides an extension torqueand then a flexion torque between the thigh link and the shank linkduring said range of motion of the thigh link and the shank linkrelative to each other, and wherein when the follower link is moved fromthe singular point away from the constraint, the constraint does notblock the motion of the follower link, and flexion and extension of thethigh link relative to the shank link are unimpeded.
 11. An artificialknee configured to be worn by a person, the artificial knee comprising:a thigh link configured to move in unison with a thigh of the person; ashank link configured to be rotatably coupled to said thigh link at afirst end of the shank link; a compression spring rotatably coupled tothe thigh link with a first end of the compression spring; a followerlink, coupled to a second end of the compression spring from one end andto the second end of the shank link from another end such that the thighlink, the shank link, the follower link, and the compression spring forma four bar linkage comprising rotary joints, wherein a singular point isa point where the compression spring and the follower link are in linewith each other; and a constraint configured to constrain the motion ofthe follower link relative to the shank link during a range of motion ofthe thigh link relative to the shank link, wherein when the followerlink is moved from said singular point toward the constraint, theconstraint blocks the follower link and the compression spring providesa force such that the force passes through the knee joint at some pointduring said range of motion of the thigh link relative to the shank linkwhen said follower link is constrained.